Excitation system for alternating current generators



July 6, 1954 MOENKE 2,683,248

EXCITATION SYSTEM FOR ALTERNATING CURRENT GENERATORS Filed Jan. 10, 1952 1:: [LI 2 E (I INVENTOR.

ALFRED R. MOENKE BY MM Patented July 6, 1954 EXCITATION SYSTEM FOR ALTERNATING CURRENT GENERATORS Alfred B. Moenke, Clifton, N. J assignor to Bendix Aviation Corporation, Teterboro, N. J a corporation of Delaware Application January 10, 1952, Serial No. 265,747

10 Claims.

The present invention relates to dynamoelectric machines and more particularly to an excitation system for dynamoelectric machines.

A copending application, Serial No. 265,858,

ing a regulating armature winding 2, a compounding armature winding 3 and a stator field Winding 4. The generator I may be driven from any suitable source such as from the engine of filed January 10, 1952, by Harold G. Haas, disan aircraft (not shown). closes and claims a system for the excitation of One end of the winding 4 is connected by outalternating current generators in which the put conductor 5 to A. C. bus 3. The other side regulating field is connected in series with the of the winding 4 is connected by conductor I to compounding field. In the aforenoted arrangeground bus 8. It is understood however that ment, the maximum ampere turns supplied by the bus 8 may not be ground inasmuch as the the bus is at no-load. In certain applications, system could be ungrounded. the ampere turns supplied by the direct current One end of the regulating Winding 2 is @011- bus to the regulating field are not sufiicient for nected to slip ring 9 which in turn is connected the no-load ampere turn requirement. In the by brush it and conductor H to positive D. C. present invention, the compounding field is arbus I?- he Other end of the Winding 2 s 00 r ng d for excitation by the bus to supply the nected to slip ring is which in turn is connected additional ampere turns necessary to meet the y b ush 4 and conductor I5 to one end of a requirements. carbon pile element 16 of a regulator H. The The excitation supplied by the compounding other end Of the carbon pile element I5 is COH- source is substantially independent of frequency 20 nected y conductor 1 t th ou ded bus 8. and is proportional to the load current of the The regulator i7 is Shown diagrammatically a generator. It is apparent that for a generator including an tu i pivoted at 20 and operating over a wide speed range, the excitaeXelting a Compressive o e upon the carbon tion supplied by the compounding source at low p le 15 u der t e e s of a Spring T speeds would be more than that required for spring 2| is arranged so as to balance the pull excitation at high speeds for the same load. At on the armature 19 by electromagnetic windings the high speeds, the voltage regulator would not 22, 23 and 24 for a predete m d u p h be able to hold the generator voltage to the winding 22 is connected across the output of a desired value. The present invention provides rectifier 5 y ClU t S 6 nd 27- One inmeans for decreasing the compounding current in; put terminal of the rectifier 25 is connec ed y with increase in frequency. a conductor 28 to the A. C. bus 6. The other in- It is an object of the invention to provide imput terminal of the rectifier 25 is connected by a proved excitation means for a generator. Conductor 29 t t d d bus 8- A vari- Another bj t of th i v ti i t provide able resistor 30 may be inserted in the conducimproved regulation for a dynamoelectric ma- 3.} tor 29 to perm t adju t e t of the Winding chine. The windings 23 and 24 are connected to the Another object of the invention is to provide output of an electronic trimmer 3|. The elecan improved dynamoelectric machine. tronic trimmer 3| may be of the type described Another object of the invention is to provide and claimed in application Seri l 690,459 improved no-load excitation for a dynamoelecof John F. Emerson filed August 14, 1946, and tric machine. assigned to Bendix Aviation Corporation, now Another object of the invention is to provide U. S. Patent No. 2,611,121. The input of the frequency compensation for the excitation of a trimmer 3| is connected by conductors 32 and dynamoelectric machine. 33 across the A. 0. output of the generator I. B+ These and other objects and features of the for the trimmer 3| is obtained from the D. C. invention will appear more fully hereinafter from bus [2 through conductor 34. a consideration of the following description taken One end of the winding 3 is connected to the in connection with the accompanying drawing end of the winding 2 adjacent the slip ring l3. wherein one embodiment of the invention is il- The other end of the winding 3 is connected by lustrated by way of example. slip ring 35, brush 3t and conductor 31 to one In the drawing the single figure of the drawof the output terminals of rectifier 38. The ing is a schematic diagram of a generator and other output terminal of the rectifier 38 is conassociated circuits embodying the invention. nected by a conductor 39 to the positive bus 12. Referring now to the drawing there is illus- The input of the rectifier 38 is connected across trated an alternating current generator I havsecondary winding 49 of current transformer 4|.

The transformer 4| has a primary winding 42 in series with the conductor 5.

The aforenoted arrangement is similar to that described and claimed in copending application Serial No. 265,859, filed by Harold G. I-Iaas.

The novel features of the present invention are directed to improve the excitation at no load and light loads, also to frequency compensation of the excitation supply.

In order to supply the ampere turn requirements for no load and light loads, the windings 3 and 2 in addition to being'connected across the output of the rectifier 38 are connected by a conductor 43, resistor 44 and rectifier 45 acrossthe D. C. supply.

In order to compensate for frequency a capacitor 46 is connected across the. secondary Winding 40 of the current transformer 4|. The capacitor 46 shunts more current from the rectifier 38 at high frequencies and prevents over excitation and resultant highv voltages.

Additional frequency compensation may be obtained by a saturable reactor 41 having an alternating current winding 48 connected in theinput of the rectifier 38 and a direct current Winding 49 connected in the output circuit of the rectifier 38.

In operation, the D. C. bus supplies the compounding field with current at no load and for light loads. When the compounding supply voltage reaches and exceeds the bus voltage, the rectifier 45 prevents a reversal of current flow to the bus. In other words, the bus can supply the compounding current only when the voltage fromv the compounding rectifier 38 is below that of the bus. The resistor 44 has a value such as to give a reasonable value of maximum pile ohms for the regulator at no load, maximum speed.

In a generator adapted for operation over a wide speed range, the excitation supplied by the compounding at the low speeds would be more than the required excitation for high speeds. Thus, the carbon pile voltage regulator would not be able to hold the voltage within the desired limits. By the provision of the capacitor 46, as the frequency rises, more current is shunted from the rectifier 38. The slope of the. frequency compensation curve can be controlled by the choice of valuesfor the capacitor.

The saturable reactor 49 permits frequency compensation to a greater extent and at the same time, the ratio of the compounding supply output current toloadcurrent will increase with load- It is understood that the reactor andcapacitor may be used either separately or together for frequency compensation depending upon the requirements of the system.

Although only one embodiment of the invention has been illustrated and described, various changes in the. form and relative arrangement of the parts may be made to suit requirements.

What is claimed is:

1. An excitation system for an alternating current generator having a pair of field windings and an output winding coupled to a load circuit, comprising an independent source of direct current connected to one of said field windings, a current transformer in series with said load, rectifier means connecting the output of said current transformer in series with both of said field windings, and means including a blocking rectifier for connecting both of saidwindings to said'independent source upon the voltage of said independent source exceeding the voltage from said current transformer.

2. The combination as set forth in claim 1 and including frequency responsive means connected in the output of said current transformer to affeet the output thereof inversely with frequency.

3. An excitation system for an alternating current generator having an excitation winding and an output winding coupled to a load circuit, comprising an independent source of direct current, means including a variable resistance element for connecting a portion of said excitation winding across said independent source, a current transformer in series with said load circuit, means including a rectifier for connecting the output of said current transformer across said excitation winding, and polarized means for connecting said excitation winding across said independent source upon the output of said current transformer being below a predetermined minimum.

4. The combination as set forth in claim. 3' and including acapacitor connected across the input of said rectifier and being so proportioned to eifect a decrease in excitation upon an increase in frequency.

5. An excitation system for a generator having a. regulating field Winding, a compounding field winding and output windings coupled to a load circuit; comprising a source of substantially constant direct current, means including. a variable resistance element for connecting said'. regulating winding across said constant direct current, means responsive to. the output voltage of said output windings for varying said resistance element to maintain said output voltage substantially constant, current responsive means connected in said output circuit to produce an outputv as a function of said current, means for connecting both of said field windings in series across said last mentioned output, andmeans including a blocking rectifier for connecting both of said field windings across said constant direct current upon the current in said output circuit being. below a predetermined value.

6. The combination as set forth in claim 5 and;

including frequency responsive means adapted to ment for. connecting said. regulating windin across said constant voltage source, means responsive to the output of said machine to vary' said resistance element to maintain said output.

having a regulating field winding, a compoundl-- ing field winding and an output winding. connected to a load, comprising a source of substantially constant potential for exciting said regulating field winding, voltage regulating means responsive to the voltage across said output winding for controllin the excitation of said regulating field winding, means including a current transformer in series with said load for producing a potential proportional to said load current for exciting both of said field windings in accordance with said load, and means including a blocking rectifier for connecting said compounding winding in series with said regulating field Winding across said constant potential source upon the potential produced by said load current being below that of the constant potential.

9. An excitation system for a variable speed alternating current generator having a pair of field windings and an output winding coupled to a load circuit, comprising a source of constant potential direct current connected to one of said field windings, a current transformer in series with said load, rectifier means connecting the output of said current transformer in series with both of said field windings, and frequency responsive means associated with the input of said rectifier to reduce the input thereof with increase in frequency.

10. An excitation system for an alternating current generator adapted to be driven at variable speeds and having a regulating field winding, a compounding field winding and an output connected to a load, comprising a source of substantially constant direct current, for energizin said regulating winding, current responsive means for producing a voltage proportional to the current in said output winding for energizing said compounding winding, and means responsive to the output frequency of said generator to decrease said last voltage upon an increase in said frequency.

References Cited in the file Of this patent UNITED STATES PATENTS Number Name Date 1,646,821 Karapetoff Oct. 25, 1927 20 1,857,174 Zucker May 10, 1932 2,610,315 McKendry et al. Sept. 9, 1952 

